1. Technical Field
Various embodiments of the present disclosure relate to MOS pass transistors and level shifters including the same.
2. Related Art
Level shifters are widely used in various semiconductor devices that perform level transition from a certain voltage level to another voltage level. Particularly, the level shifters may be used to convert a low voltage level to a high voltage level. For example the level shifters may be used to drive output pins of integrated circuits to a logic level which is higher than an Internal logic level of the integrated circuits. In some cases, the level shifters may be used to convert a high voltage level to a low voltage level,
In general, the level shifters have been used to drive word lines connected to control gates of memory cell transistors constituting a cell array, which is employed in nonvolatile memory devices such as electrically erasable programmable read only memory (EEPROM) devices, flash EEPROM devices, nonvolatile random access memory (NOVRAM) devices, one-time programmable (OTP) devices or multi-time programmable (MTP) devices. A write-in voltage higher than a read-out voltage has to be supplied to the memory cell transistors in order to write data into the memory cell transistors. For example, while the read-out voltage for example, 1.8 volts to 5.5 volts, which is equal to or lower than a power supply voltage VDD that is, a digital supply voltage, is applied to the control gates of the memory cell transistors in a read mode the write-in voltage for example 10 volts to 12.5 volts, which is higher than the power supply voltage VDD may be applied to the control gates of the memory cell transistors in a program mode. In general, the high voltage such as the write-in voltage also, referred to as a program voltage, used in the program mode is generated by voltage multiplier circuits such as charge pumping circuits disposed in chips. The on-chip charge pumping circuits may raise a unit price of a chip and may cause high power consumption of the chip. Thus, the level shifters have been used for both the program mode that is, a write mode, and the read mode. In such a case, an output supply voltage level VPP of the level shifters may be lowered in the read mode.